Metallization and stringing for back-contact solar cells

ABSTRACT

Metallization and stringing methods for back-contact solar cells, and resulting solar cells, are described. In an example, in one embodiment, a method involves aligning conductive wires over the back sides of adjacent solar cells, wherein the wires are aligned substantially parallel to P-type and N-type doped diffusion regions of the solar cells. The method involves bonding the wires to the back side of each of the solar cells over the P-type and N-type doped diffusion regions. The method further includes cutting every other one of the wires between each adjacent pair of the solar cells.

TECHNICAL FIELD

Embodiments of the present disclosure are in the field of renewableenergy and, in particular, include metallization and stringingtechniques for back-contact solar cells, and the resulting solar cellsand modules.

BACKGROUND

Photovoltaic cells, commonly known as solar cells, are well knowndevices for direct conversion of solar radiation into electrical energy.Generally, solar cells are fabricated on a semiconductor wafer orsubstrate using semiconductor processing techniques to form a p-njunction near a surface of the substrate. Solar radiation impinging onthe surface of, and entering into, the substrate creates electron andhole pairs in the bulk of the substrate. The electron and hole pairsmigrate to p-doped and n-doped regions in the substrate, therebygenerating a voltage differential between the doped regions. The dopedregions are connected to conductive regions on the solar cell to directan electrical current from the cell to an external circuit coupledthereto.

Efficiency is an important characteristic of a solar cell as it isdirectly related to the capability of the solar cell to generate power.Likewise, efficiency in producing solar cells is directly related to thecost effectiveness of such solar cells. Accordingly, techniques forincreasing the efficiency of solar cells, or techniques for increasingthe efficiency in the manufacture of solar cells, are generallydesirable. Some embodiments of the present disclosure allow forincreased solar cell manufacture efficiency by providing novel processesfor fabricating solar cell structures. Some embodiments of the presentdisclosure allow for increased solar cell efficiency by providing novelsolar cell structures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a plan view of the back side of a solar cell havingwire-based metallization, in accordance with an embodiment of thepresent disclosure.

FIG. 1B illustrates a cross-sectional view corresponding to the solarcell of FIG. 1A.

FIG. 2 is a flowchart listing operations in a method of metallizationand stringing for back-contact solar cells, in accordance with anembodiment of the present disclosure.

FIGS. 3A-3E and 4A-4E illustrate views of various stages in ametallization and stringing method for back-contact solar cells,corresponding to the operations in the method of FIG. 2, in accordancewith an embodiment of the present disclosure, wherein:

FIG. 3A illustrates a back-side view of adjacent solar cells that are tobe stringed together, the solar cells including alternating P-type andN-type doped diffusion regions that are substantially parallel to anedge of the solar cells;

FIG. 3B illustrates a back-side view of the adjacent solar cells of FIG.3A following attachment of a non-conductive shield to the back sides ofthe adjacent solar cells;

FIG. 3C illustrates a back-side view of the adjacent solar cells of FIG.3B following alignment of conductive wires over the back sides of theadjacent solar cells, wherein the wires are aligned substantiallyparallel to the P-type and N-type doped diffusion regions of the solarcells;

FIG. 3D illustrates a back-side view of the adjacent solar cells of FIG.3C following bonding of the conductive wires to the back sides ofadjacent solar cells;

FIG. 3E illustrates a back-side view of the adjacent solar cells of FIG.3D following the cutting of every other one of the wires between eachadjacent pair of the solar cells;

FIG. 4A illustrates a back-side view of adjacent solar cells that are tobe stringed together, the adjacent solar cells including alternatingP-type and N-type doped diffusion regions that are at a non-zero anglerelative to the edges of the solar cells;

FIG. 4B illustrates a back-side view of the adjacent solar cells of FIG.4A following attachment of a non-conductive shield to the back sides ofthe adjacent solar cells;

FIG. 4C illustrates a back-side view of the adjacent solar cells of FIG.4B following alignment of conductive wires over the back sides ofadjacent solar cells, wherein the wires are aligned substantiallyparallel to P-type and N-type doped diffusion regions of the solarcells;

FIG. 4D illustrates a back-side view of the adjacent solar cells of FIG.4C following bonding of the conductive wires to the back sides of theadjacent solar cells; and

FIG. 4E illustrates a back-side view of the adjacent solar cells of FIG.4D following the cutting of every other one of the wires between eachadjacent pair of the solar cells.

FIG. 5 illustrates a string of solar cells, in accordance with anembodiment of the present disclosure.

FIG. 6 illustrates a system for stringing together solar cells, inaccordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature andis not intended to limit the embodiments of the subject matter or theapplication and uses of such embodiments. As used herein, the word“exemplary” means “serving as an example, instance, or illustration.”Any implementation described herein as exemplary is not necessarily tobe construed as preferred or advantageous over other implementations.Furthermore, there is no intention to be bound by any expressed orimplied theory presented in the preceding technical field, background,brief summary or the following detailed description.

This specification includes references to “one embodiment” or “anembodiment.” The appearances of the phrases “in one embodiment” or “inan embodiment” do not necessarily refer to the same embodiment.Particular features, structures, or characteristics may be combined inany suitable manner consistent with this disclosure.

Terminology. The following paragraphs provide definitions and/or contextfor terms found in this disclosure (including the appended claims):

“Comprising.” This term is open-ended. As used in the appended claims,this term does not foreclose additional structure or steps.

“Configured To.” Various units or components may be described or claimedas “configured to” perform a task or tasks. In such contexts,“configured to” is used to connote structure by indicating that theunits/components include structure that performs those task or tasksduring operation. As such, the unit/component can be said to beconfigured to perform the task even when the specified unit/component isnot currently operational (e.g., is not on/active). Reciting that aunit/circuit/component is “configured to” perform one or more tasks isexpressly intended not to invoke 35 U.S.C. §112, sixth paragraph, forthat unit/component.

“First,” “Second,” etc. As used herein, these terms are used as labelsfor nouns that they precede, and do not imply any type of ordering(e.g., spatial, temporal, logical, etc.). For example, reference to a“first” solar cell does not necessarily imply that this solar cell isthe first solar cell in a sequence; instead the term “first” is used todifferentiate this solar cell from another solar cell (e.g., a “second”solar cell).

“Coupled”—The following description refers to elements or nodes orfeatures being “coupled” together. As used herein, unless expresslystated otherwise, “coupled” means that one element/node/feature isdirectly or indirectly joined to (or directly or indirectly communicateswith) another element/node/feature, and not necessarily mechanically.

“Inhibit”—As used herein, inhibit is used to describe a reducing orminimizing effect. When a component or feature is described asinhibiting an action, motion, or condition it may completely prevent theresult or outcome or future state completely. Additionally, “inhibit”can also refer to a reduction or lessening of the outcome, performance,and/or effect which might otherwise occur. Accordingly, when acomponent, element, or feature is referred to as inhibiting a result orstate, it need not completely prevent or eliminate the result or state.

In addition, certain terminology may also be used in the followingdescription for the purpose of reference only, and thus are not intendedto be limiting. For example, terms such as “upper”, “lower”, “above”,and “below” refer to directions in the drawings to which reference ismade. Terms such as “front”, “back”, “rear”, “side”, “outboard”, and“inboard” describe the orientation and/or location of portions of thecomponent within a consistent but arbitrary frame of reference which ismade clear by reference to the text and the associated drawingsdescribing the component under discussion. Such terminology may includethe words specifically mentioned above, derivatives thereof, and wordsof similar import.

Metallization and stringing methods for back-contact solar cells, andthe resulting solar cells and modules, are described herein. In thefollowing description, numerous specific details are set forth, such asspecific process flow operations, in order to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to one skilled in the art that embodiments of the presentdisclosure may be practiced without these specific details. In otherinstances, well-known fabrication techniques, such as lithography andpatterning techniques, are not described in detail in order to notunnecessarily obscure embodiments of the present disclosure.Furthermore, it is to be understood that the various embodiments shownin the figures are illustrative representations and are not necessarilydrawn to scale.

Disclosed herein are strings of solar cells. In one embodiment, a stringof solar cells includes a plurality of back-contact solar cells. Each ofthe plurality of back-contact solar cells includes alternating P-typeand N-type doped diffusion regions. A plurality of conductive wires isdisposed over a back surface of each of the plurality of solar cells,wherein each of the plurality of wires is substantially parallel to theP-type and N-type doped diffusion regions of each of the plurality ofsolar cells. Every other one of the plurality of wires is cut in aregion between each adjacent pair of the plurality of solar cells.

In one embodiment, a string of solar cells includes a plurality ofback-contact solar cells, wherein each of the plurality of back-contactsolar cells includes alternating P-type and N-type doped diffusionregions. The plurality of back-contact solar cells includes end solarcells and inner solar cells between the end solar cells. One of theP-type diffusion regions of each of the inner solar cell is locatedopposite one of the N-type diffusions of an adjacent solar cell along aline parallel to the P-type and N-type regions. The string of solarcells also includes a plurality of conductive wires disposed over a backsurface of each of the plurality of solar cells. Each of the pluralityof wires is substantially parallel to the P-type and N-type dopeddiffusion regions of each of the plurality of solar cells. Every otherone of the plurality of wires is cut in a region between each adjacentpair of the plurality of solar cells.

Also disclosed herein are methods of fabricating strings of solar cells.In one embodiment a method of electrically coupling solar cells involvesaligning conductive wires over the back sides of adjacent solar cells.The wires are aligned substantially parallel to P-type and N-type dopeddiffusion regions of the solar cells. The method involves bonding thewires to the back side of each of the solar cells over the P-type andN-type doped diffusion regions. The method further involves cuttingevery other one of the wires between each adjacent pair of the solarcells.

Also disclosed herein are systems for electrically coupling solar cells.In one embodiment, a system includes a wire support to align conductivewires substantially parallel with P-type and N-type doped diffusionregions of each of the solar cells. The system also includes a welder tobond the wires to the back side of each of the solar cells over theP-type and N-type doped diffusion regions. The system also includes acutter to sever every other one of the wires between each adjacent pairof the solar cells.

Thus, one or more embodiments described herein are directed tometallization and stringing techniques. According to embodiments, wiresmay be used to string back-contact solar cells together instead ofpatterned cell interconnects. The wires can also serve as metallizationto collect current across the cells, either by themselves, or inconjunction with a first level metallization on the solar cells.

To provide context, techniques for stringing together back-contact solarcells can be different than techniques for stringing togetherfront-contact cells. In an example, for back-contact cells, metalfingers for each polarity (N and P) can be connected to a single busbarat the edge of the cell. Cell interconnects can then be soldered fromthe “P busbar” (e.g., the busbar connected to the metal finger for agiven P-type region) of one cell to the “N busbar” (e.g., the busbarconnected to the metal finger for a given N-type region) of the nextsolar cell.

The space used by such busbars on the solar cells reduces the overallefficiency of the solar cells. Furthermore, the process of forming themetal fingers and the busbars on the cell can be costly. Stringingtogether front-contact solar cells (in contrast to embodiments describedherein, which include methods for stringing together back-contact solarcells) may involve the use of metal ribbons weaving from the back sideof one cell to the front side of the next cell. In other words, betweentwo front contact cells, a ribbon can go underneath one cell and acrossthe top of another adjacent cell (e.g., the next cell). Weaving fromfront to back for front-contact cells can pose manufacturingdifficulties (e.g., alignment difficulties, etc.).

According to embodiments, instead of using busbars to collect thecurrent throughout each cell, each finger (e.g., P-type doped diffusionregions or N-type doped diffusion regions) of one cell is directlyconnected to the corresponding finger (e.g., a finger of oppositepolarity) of the next cell using continuous conductive wires. Theribbons are first attached across some or all cells of the entire string(e.g., in a continuous string), shorting each pair of solar cells. Everyother wire is subsequently cut between cells in order to restoreseparate P and N electrodes. For example, P and N electrodes areseparate but connected back and forth if every other wire is not cut.Every other wire connects the P electrodes of a first cell to the Nelectrodes of a second cell. The other wires connect the N electrodes ofthe first cell to the P electrodes of the second cell. The pair of cellsis therefore shorted if one of the two sets of wires is not cut.Therefore, cutting one of the two sets of wires between a given pair ofcells can restore separate P and N electrodes.

For example, FIGS. 1A and 1B illustrate a plan view of the back side ofa solar cell having wire-based metallization, and a correspondingcross-sectional view, in accordance with an embodiment of the presentdisclosure.

Referring to FIGS. 1A and 1B, a portion 100 of a solar cell includes asubstrate 102 having a back surface 104 and an opposing light-receivingsurface 106. A plurality of alternating N-type and P-type semiconductorregions (one such regions shown as 108) is disposed in or above the backsurface 104 of the substrate 102. A conductive contact structure isdisposed on the plurality of alternating N-type and P-type semiconductorregions 108. The conductive contact structure includes a plurality ofconductive wires (one conductive wire shown as 110). Each conductivewire 110 is bonded to the solar cell at bonding points. Each conductivewire 110 of the plurality of conductive wires is parallel along a firstdirection 112 to form a one-dimensional layout of a metallization layerfor the portion 100 of a solar cell, examples of which are described ingreater detail below in association with FIGS. 3A-3E and 4A-4E.

In an embodiment, as is depicted in FIGS. 1A and 1B, the conductivecontact structure further includes a metal seed layer 114 (e.g., an Mllayer) disposed between the plurality of alternating N-type and P-typesemiconductor regions 108 and the plurality of conductive wires 110. Insome embodiment including a metal seed layer 114, the conductive wiresmay be soldered or welded (e.g., with a laser) to the metal seed layer114, as is described in more detail below with respect to FIGS. 3D and4D.

In an exemplary process flow, FIG. 2 is a flowchart listing operationsin a method of metallization and stringing for back-contact solar cells,in accordance with an embodiment of the present disclosure. FIGS. 3A-3Eand 4A-4E illustrate views of various stages in a metallization andstringing method for back-contact solar cells, corresponding to theoperations in the method of FIG. 2, in accordance with an embodiment ofthe present disclosure

FIG. 3A illustrates a back-side view of adjacent solar cells 302 thatare to be stringed together, including alternating P-type dopeddiffusion regions 304 and N-type doped diffusion regions 306. In onesuch embodiment, each of the plurality of solar cells 302 issubstantially rectangular, and the P-type doped diffusion regions 304and the N-type doped diffusion regions 306 are substantially parallel tothe edges 301, 303 of the solar cells 302. A solar cell that issubstantially rectangular could be, for example, a square, or anotherrectangular shape, and may have standard, cut, or rounded corners. Asillustrated in FIG. 3A, the solar cells 302 are asymmetric in the sensethat the solar cells 302 end with a P finger on one side (e.g., side303) and an N finger on the opposite side (e.g., side 301). Theasymmetric solar cells can then be placed in alternating orientationsalong the string, as illustrated in FIG. 3A. The asymmetric solar celldesign together with the alternating orientations along the stringenable the use of wires that are parallel to the edges 301, 303 of thesolar cells because the P finger on one of the solar cells is directlyacross from the N finger of the adjacent solar cell, as is explainedbelow with respect to FIG. 3C.

In another embodiment, an oblique finger design is used, as illustratedin FIG. 4A. FIG. 4A also illustrates a back-side view of adjacent solarcells 402 that are to be stringed together, including alternating P-typedoped diffusion regions 404 and N-type doped diffusion regions 406.However, in contrast to FIG. 3A, the alternating P-type doped diffusionregions 404 and N-type doped diffusion regions 406 are at a non-zeroangle relative to the edges 403 of the substantially rectangular solarcells 402. Thus, in one embodiment, the P-type doped diffusion regions404 and N-type doped diffusion regions 406 are actually formed at anon-zero angle in or over the substrate. In one embodiment, thealternating P-type doped diffusion regions 404 and N-type dopeddiffusion regions 406 are at an angle in a range of 1 to 25 degreesrelative to the edges 401, 403 of each of the plurality of solar cells.In one such embodiment, the alternating P-type doped diffusion regions404 and N-type doped diffusion regions 406 are at an angle in the rangeof 1 to 5 degrees relative to edges of each of the plurality of solarcells.

According to one embodiment, in an oblique finger design, each of thesolar cells 402 can have the same configuration and number ofalternating P-type doped diffusion regions 404 and N-type dopeddiffusion regions 406. Therefore, the solar cells 402 are placed havingthe same alignment in a string (e.g., not the alternating orientationdescribed with respect to FIG. 3A). However, with an oblique fingerdesign, the management of wires may be more complex than with theparallel finger design.

Referring to FIG. 3B and corresponding operation 202 of flowchart 200, amethod of metallization and stringing includes attaching anon-conductive shield 308 to the back sides of the adjacent solar cells302. Similarly, FIG. 4B illustrates a back-side view of the adjacentsolar cells 402 of FIG. 4A following attachment of a non-conductiveshield 408 to the back sides of the adjacent solar cells 402. Thenon-conductive shield 308 may be a non-conductive tape or other suitablenon-conductive shield or cover. The non-conductive shield may serve tohide the ribbons when viewed from the front. Thus, the non-conductiveshield covers exposed sections of the wires between each adjacent pairof the plurality of solar cells. Therefore, according to embodiments,the non-conductive shield includes a material that is substantiallyopaque to sufficiently cloak the wires when viewed from the front. Thenon-conductive shield may also assist in alignment of the solar cells,and/or holding the solar cells 302 together. The non-conductive shield308 may include materials such as polypropylene or polyethylene, and canfurther include an adhesive layer like an acrylate. A non-conductiveshield with an adhesive layer can be beneficial to assist in alignment.The non-conductive shield 408 may be similar to, or the same as, thenon-conductive shield 308. Although a non-conductive shield may bebeneficial for the reasons explained above, other embodiments may notinclude a non-conductive shield.

Referring to FIG. 3C and corresponding operation 204 of the flowchart200, the method of metallization and stringing includes aligningconductive wires 310 over the back sides of adjacent solar cells 302. Inone embodiment, the wires 310 are aligned substantially parallel to theP-type doped diffusion regions 304 and N-type doped diffusion regions306 of the solar cells 302. The wires 310 can have a cross-sectionalshape that is round, flattened (e.g., ribbons), slightly flattened, oranother shape. Round wires may be beneficial because they can be rolledor twisted. In an embodiment involving the alignment and placement ofround wires, the wires can be flattened prior to or during bonding thewires to the back side of each of the solar cells.

Conductive wires include an electrically conducting material (e.g., ametal such as copper, aluminum, or another suitable conductive material,with or without a coating such as tin, silver, nickel or an organicsolderability protectant). In the embodiment illustrated in FIG. 3C, thenumber of wires is equal to (or approximately equal to) the number ofdiffusion regions of each of the plurality of solar cells. In one suchembodiment, a single wire is aligned over each of the P-type dopeddiffusion regions 304 and N-type doped diffusion regions 306 of thesolar cells 302. According to one embodiment, each of the wires 310 isroughly centered over one of the P-type doped diffusion regions 304 andN-type doped diffusion regions 306 of the solar cells 302

As illustrated in FIG. 3C, the wires 310 can be aligned so that they aresubstantially parallel to the edges 301, 303 of the plurality of solarcells 302. In an embodiment where the P-type and N-type doped diffusionregions are not parallel to the edges of the solar cells, such as inFIG. 4C, the wires 410 would also not be aligned parallel to the edges401, 403 of the solar cells 402. For example, if the P-type dopeddiffusion regions 404 and the N-type doped diffusion regions 406 aredisposed at an angle in the range of 1 to 25 degrees, the wires would bealigned parallel with the P-type doped diffusion regions 404 and theN-type doped diffusion regions 406, and thus would also be disposed atan angle in a range of 1 to 25 degrees relative to edges 401, 403 ofeach of the plurality of solar cells 402.

Turning again to FIG. 3C, the wires can be aligned via a variety ofmechanisms. For example, in one embodiment, aligning the conductivewires 310 over the back sides of adjacent solar cells 302 involves useof a grooved roller (such as the grooved roller 602 depicted in FIG. 6,which is described in further detail below). Other mechanisms may beused to align the conductive wires 310 over the P-type doped diffusionregions 304 and N-type doped diffusion regions 306 of the solar cells302 instead of, or in addition to, a grooved roller. For example,according to one embodiment, a reed, or other mechanism suitable foraligning and guiding the conductive wires may be used. When aligningwires over a solar cell that is not the first solar cell, the fact thatthe wires are bonded to the first solar cell can assist in alignment ofthe wires over the subsequent solar cells, in accordance with anembodiment.

After aligning the conductive wires 310, the method illustrated in FIG.2 involves bonding the conductive wires to the back side of the solarcells 302 the P-type doped diffusion regions 304 and N-type dopeddiffusion regions 306 of the solar cells 302, at operation 204. FIG. 3Dillustrates a back-side view of the adjacent solar cells 302 of FIG. 3Cfollowing bonding of the conductive wires 310 to the back sides of theadjacent solar cells 302. Similarly, FIG. 4D illustrates a back-sideview of the adjacent solar cells 402 of FIG. 4C following bonding of theconductive wires 410 to back sides of adjacent solar cells 402.

Referring to FIG. 3D, according to one embodiment, the conductive wiresare bonded at a number of locations 311 over the P-type doped diffusionregions 304 and N-type doped diffusion regions 306. The number of bondsmay depend on the cell size and the bonding technique used. For example,the conductive wires may be bonded at a few locations for soldering, inaccordance with an embodiment. In another example, the conductive wiresmay be bonded at more than a hundred locations for laser welding, inaccordance with an embodiment. In one embodiment, a continuous bond isformed. As mentioned above, in one embodiment, a metal seed layer (e.g.,the metal seed layer 114 of FIGS. 1A and 1B) is disposed over the P-typedoped diffusion regions 304 and N-type doped diffusion regions 306. Inone such embodiment, the conductive wires 310 may be bonded to the metalseed layer. In an embodiment without a metal seed layer, the conductivewires 310 may be bonded directly to the P-type doped diffusion regions304 and N-type doped diffusion regions 306.

A variety of bonding methods may be used, such as, for example,thermo-compression bonding, laser welding, soldering, and/or theapplication of a conductive adhesive. In one embodiment, bondinginvolves contacting the wires to the back side of one the solar cellswith a roller (e.g., by pressing/applying pressure to the wires with theroller), and welding the wires in the locations 311 with a laser. In onesuch embodiment, the laser can emit laser beams that are transmittedthrough the roller while the roller applies sufficient pressure tomaintain alignment and create a bond. In another embodiment, the wires310 contact the back side of a solar cell by the application of pressureby two rollers. In one such embodiment, the two rollers are spacedsufficiently far apart to allow for laser beams to pass between the tworollers to bond the wires at the locations 311 while the two rollersapply sufficient pressure to maintain alignment and create a bond.

Referring to FIG. 3E and corresponding operation 206 of the flowchart200, the method of metallization and stringing includes cutting everyother one of the wires 310 between each adjacent pair of the solar cells302. Similarly, FIG. 4E illustrates a back-side view of the adjacentsolar cells 402 of FIG. 4D following the cutting of every other one ofthe wires 410 between the adjacent pair of solar cells 402. Asillustrated in FIG. 3E, the wires 310 are cut at the locations 312, suchthat all of the wires connected to the P-type diffusion on one side of asolar cell 302, and all of the wires connected to the N-type diffusionof the opposite side of the solar cell are cut. Prior to cutting thewires 310 in the locations 312, the pair of solar cells are shorted.Cutting the wires 310 enables electrically coupling the solar cells forcollection of current from the solar cell string. Cutting the wires 310in the locations 312 may involve any wire cutting technique. For examplethe wires 310 may be cut in the locations 312 with a laser or a blade.Although the FIGS. 3A-3E and 4A-4E illustrate only two solar cells, asolar cell string can include any number of solar cells stringedtogether (e.g., 2 or more solar cells stringed together). The process iscontinuous in the sense that arbitrarily long strings of solar cells canbe made.

FIG. 5 illustrates one example of a string of solar cells, in accordancewith an embodiment of the present disclosure. The solar cell string 500Aillustrated in FIG. 5 includes a plurality of solar cells 502 that areelectrically coupled together in series. The solar cell string 500A hastwo end solar cells 501, and inner solar cells 503 connected in seriesbetween the two end solar cells 501. Each of the two end solar cells 501is electrically coupled with a busbar 514. At each of the end solarcells 501, every other one of the wires is coupled with a busbar 514 tocouple only one of the two electrodes of the end solar cell, either theP-type doped diffusion regions 504 or the N-type doped diffusion regions506. In one embodiment, the coupling of every other one of the wiresfrom an end solar cell 501 with a busbar 514 may be achieved by firstcutting all the wire at each end of the string, and connecting only thewires for either the P-type or N-type doped diffusion regions.Alternatively, all the wires for an end solar cell 501 may first beconnected to a busbar 514, and then every other wire can be cut.

Only the end solar cells 501 are connected to a busbar 514, in contrastto other stringing techniques which can involve attaching busbar(s) toeach solar cell, according to some embodiments. The busbars 514 maycouple the solar string 500A with another solar string (e.g., such asthe solar string 500B), or to another circuit (e.g., a circuit outsidethe module through a junction box).

As illustrated in FIG. 5, in one embodiment, a given cut section of wireis to electrically couple at most two solar cells together in series,wherein the P-type doped diffusion area of one of the two solar cells isconnected to the N-type doped diffusion area of the other solar cell.However, other embodiments may include more than two solar cells beingcoupled together with a given cut section of wire. For example, if solarcells are connected in parallel, it is possible to connect more than twocells with a given cut section of wire. Also as illustrated in FIG. 5,in one embodiment, a cut section of wire that electrically couples anend solar cell 501 to the busbar 514 couples a single solar cell to thebusbar 514. However, as mentioned above, in embodiments that connectsolar cells in parallel, a given cut section of wire may connect morethan a single solar cell to the busbar. Thus, a solar string can becreated using the plurality of wires 510 by aligning and bonding thewires over the P-type and N-type doped diffusion regions of each of thesolar cells, followed by cutting some of the wires to achieve thedesired configuration of solar cells in a string.

FIG. 6 illustrates a system for stringing together solar cells to createa solar cell string (such as the string 500A of FIG. 5), in accordancewith an embodiment of the present disclosure. According to oneembodiment, a system 600 for electrically coupling solar cells includesa wire support to align conductive wires substantially parallel withP-type and N-type doped diffusion regions of each of the solar cells. Inthe embodiment illustrated in FIG. 6, the wire support includes agrooved roller 602 to guide and support the wires 310 into the system600, and ensure the desired alignment with the P-type and N-type dopeddiffusion regions. The desired alignment for the wires may be parallelwith edges of the solar cells, as explained above with respect to FIGS.3A-3E. In another embodiment, the wires are aligned at a non-zero anglerelative to the edges of the solar cells. Although a grooved roller 602is illustrated in FIG. 6, other embodiments may include other wiresupport and alignment mechanisms.

For example, a reed may be used to align the wires prior to bonding onthe back sides of the solar cells 302. A reed includes a structure thatresembles a comb, in that it has a plurality of teeth that separateslots through which the wires can pass. For example, a reed can includea slot for each of the wires, which can enable separating the wires fromeach other and guiding them into the desired position. Other alignmentand support mechanisms capable of aligning a plurality of wires over asolar cell may also be used.

The system 600 also includes a welder 606 to bond the wires to the backside of each of the solar cells 302 over the P-type and N-type dopeddiffusion regions. For example, the welder 606 can form bonds at aplurality of locations, such as illustrated in FIGS. 3D and 4D. In oneembodiment, the welder 606 includes a laser welder. Other weldingtechniques may also be used, such as, for example, thermo-compressionbonding, soldering, (e.g., the use of a low-melting point metal for asoldering operation), or application of a conductive adhesive. In oneembodiment, one or more rollers are used to hold the wires in placeduring laser bonding. For example, as illustrated in FIG. 6, a roller604 applies pressure to the wires 310 as the welder 606 bonds the wires310 to the solar cells 302. As mentioned above, in one embodimentinvolving a laser welder, the roller 604 is substantially transparent tothe laser beams from the laser welder. Therefore, the laser welder ispositioned such that the laser beams pass through the roller 604 to bondthe wires 310 to the back side of a solar cell. A transparent roller mayinclude a quartz roller, or a roller made from another material that issubstantially transparent to the laser.

In another embodiment, more than one roller 604 is used to hold thewires in place and properly aligned while the wires are bonded to theback side of a solar cell. For example, in one embodiment, two rollersare used. In one such embodiment, the two rollers are separated byenough space to enable a laser welder to form a bond between the wiresand the solar cell by directing a laser beam between the two rollers.Thus, in one such embodiment, the rollers do not need to be transparentto the laser (e.g., the rollers can be opaque). In an embodiment usinground wires (or wires having other shapes, which are to be flattened),the roller 604 can be used to apply sufficient pressure to flatten thewire before or during bonding. Other flattening mechanisms may be usedprior to or during bonding. After the wires have been bonded to onesolar cell, the alignment and bonding may be simplified by the fact thatthe wires are properly aligned on the preceding solar cell. For example,the wires are held in place at one end of the solar cell by the welds onthe previous solar cell, and held in place at the other end of the solarcell by the roller 604 (or other support and/or alignment mechanism).Thus, in one embodiment, prior to cutting the wires on a first solarcell, the wires are aligned over and bonded to the next solar cell. Inone embodiment, the wires may be bonded to the solar cells for theentire string prior to severing any of the wires, in accordance with anembodiment.

The system 600 also includes a cutter 608 to sever every other one ofthe wires between each adjacent pair of the solar cells, in accordancewith the methods described above. The cutter 608 can include anysufficiently precise mechanism for cutting wire, such as a singulationblade or laser. The system 600 may further include a translation orconveyor mechanism to move the solar cells 302 through the system. Asolar cell that has been processed by the system 600 may have featuressimilar to the solar cell 302 of FIG. 3E and the solar cell 402 of FIG.4E. The system may also include a second cutter 610, which isillustrated as a blade in FIG. 6. The cutter 610 may sever all the wireswhen the end of a solar string is reached. Some of the cut wires maythen be connected to a busbar, as described above with respect to FIG.5. Accordingly, the system 600 may be used to string together solarcells to form a solar cell string such as illustrated in FIG. 5.

Thus, methods of metallization and stringing for back-contact solarcells, and the resulting solar cells, have been disclosed.

Although specific embodiments have been described above, theseembodiments are not intended to limit the scope of the presentdisclosure, even where only a single embodiment is described withrespect to a particular feature. Examples of features provided in thedisclosure are intended to be illustrative rather than restrictiveunless stated otherwise. The above description is intended to cover suchalternatives, modifications, and equivalents as would be apparent to aperson skilled in the art having the benefit of this disclosure.

The scope of the present disclosure includes any feature or combinationof features disclosed herein (either explicitly or implicitly), or anygeneralization thereof, whether or not it mitigates any or all of theproblems addressed herein. Accordingly, new claims may be formulatedduring prosecution of this application (or an application claimingpriority thereto) to any such combination of features. In particular,with reference to the appended claims, features from dependent claimsmay be combined with those of the independent claims and features fromrespective independent claims may be combined in any appropriate mannerand not merely in the specific combinations enumerated in the appendedclaims.

1. A string of solar cells comprising: a plurality of back-contact solarcells, wherein each of the plurality of back-contact solar cellscomprises alternating P-type and N-type doped diffusion regions; and aplurality of conductive wires disposed over a back surface of each ofthe plurality of solar cells, wherein each of the plurality ofconductive wires is substantially parallel to the P-type and N-typedoped diffusion regions of each of the plurality of solar cells; whereinevery other one of the plurality of conductive wires is cut in a regionbetween each adjacent pair of the plurality of solar cells.
 2. Thestring of solar cells of claim 1, wherein each of the plurality of solarcells is substantially rectangular, and wherein the P-type dopeddiffusion regions, the N-type doped diffusion regions, and the pluralityof conductive wires are substantially parallel to a first edge of eachof the plurality of solar cells.
 3. The string of solar cells of claim1, wherein each of the plurality of solar cells is substantiallyrectangular, and wherein the P-type doped diffusion regions, the N-typedoped diffusion regions, and the plurality of conductive wires aredisposed at a non-zero angle relative to edges of each of the pluralityof solar cells.
 4. The string of solar cells of claim 3, wherein theP-type doped diffusion regions, the N-type doped diffusion regions, andthe plurality of conductive wires are disposed at an angle in a range of1 to 25 degrees relative to edges of each of the plurality of solarcells.
 5. The string of solar cells of claim 1, wherein a given cutsection of wire of the plurality of conductive wires is to electricallycouple at most two solar cells together in series, wherein the P-typedoped diffusion regions of one of the two solar cells is connected tothe N-type doped diffusion regions of the other of the two solar cells.6. The string of solar cells of claim 1, further comprising: aconductive busbar at an end of the string of solar cells, wherein theconductive busbar is electrically coupled with every other one of theplurality of conductive wires, and wherein the conductive busbar is toelectrically couple the string with another string of solar cells. 7.The string of solar cells of claim 6, wherein a cut section of wire ofthe plurality of conductive wires that is to electrically couple the endof the string of solar cells to the conductive busbar is to couple asingle solar cell to the conductive busbar.
 8. The string of solar cellsof claim 1, wherein a number of the plurality of conductive wires isequal to a number of diffusion regions of each of the plurality of solarcells.
 9. The string of solar cells of claim 1, further comprisingnon-conductive shields disposed between and coupling back sides of eachadjacent pair of the plurality of solar cells.
 10. The string of solarcells of claim 9, wherein the non-conductive shields cover exposedsections of the plurality of conductive wires between each adjacent pairof the plurality of solar cells.
 11. A method of electrically couplingsolar cells, the method comprising: aligning conductive wires over backsides of adjacent solar cells, wherein the conductive wires are alignedsubstantially parallel to P-type and N-type doped diffusion regions ofthe solar cells; bonding the conductive wires to the back side of eachof the solar cells over the P-type and N-type doped diffusion regions;and cutting every other one of the conductive wires between eachadjacent pair of the solar cells.
 12. The method of claim 11, whereinaligning the conductive wires comprises aligning the conductive wiressubstantially parallel to a first edge of each of the plurality of solarcells.
 13. The method of claim 11, wherein aligning the conductive wirescomprises aligning the conductive wires at a non-zero angle relative toedges of each of the plurality of solar cells, wherein the P-type dopeddiffusion regions and the N-type doped diffusion regions are at thenon-zero angle relative to edges of each of the plurality of solarcells.
 14. The method of claim 11, wherein cutting every other one ofthe conductive wires comprises cutting the conductive wires toelectrically couple at most two solar cells together in series with agiven cut section of wire, wherein the given cut section of wire is toconnect the P-type doped diffusion regions of one of the two solar cellsto the N-type doped diffusion regions of the other of the two solarcells.
 15. The method of claim 11, wherein the electrically coupledsolar cells form a string of solar cells, the method further comprising:electrically coupling a conductive busbar with each wire bonded to anend solar cell of the string; cutting every other one of the conductivewires between the conductive busbar and the end solar cell; andelectrically coupling the conductive busbar with another string of solarcells.
 16. The method of claim 15, wherein cutting every other one ofthe conductive wires between the conductive busbar and the end solarcell comprises electrically coupling a single solar cell of the stringof solar cells with the conductive busbar.
 17. The method of claim 11,further comprising attaching a non-conductive shield to back sides ofthe solar cells between each adjacent pair of the solar cells, hidingexposed sections of the conductive wires when viewed from front sides ofthe solar cells.
 18. The method of claim 11, wherein cutting the everyother one of the conductive wires between each adjacent pair of thesolar cells comprises cutting the every other one of the conductivewires with a laser or blade.
 19. A system for electrically couplingsolar cells, the system comprising: a wire support to align conductivewires substantially parallel with P-type and N-type doped diffusionregions of each of the solar cells; a welder to bond the conductivewires to the back side of each of the solar cells over the P-type andN-type doped diffusion regions; and a cutter to sever every other one ofthe conductive wires between each adjacent pair of the solar cells. 20.The system of claim 19, wherein the wire support comprises a groovedroller or a reed to align the conductive wires substantially parallel toa first edge of each of the plurality of solar cells.